1. Field of the Invention
The present invention relates to a microarrayer for sequencing a large number of biological samples such as DNA fragments or oligonucleotides on substrates.
2. Description of the Related Art
Currently, technological development for analyzing the whole gene functions of a wide variety of organisms is in progress. DNA microarrays (that is, DNA chips) are of a large number of spots including DNA fragments or the like sequenced on glass slides or silicon substrates. Such DNA microarrays are very effective in analyzing gene expressions, genetic mutations, genetic variations, and the like.
Each substrate generally measures 1 cm2 to several tens of cm2, and several thousands to several hundred thousands of spots of DNA fragments are sequenced in this area. Each of the DNA fragments on the substrate is investigated with a fluorescent-labeled DNA complementary thereto. Fluorescence is generated when hybridization is produced between the DNA fragment on the substrate and the fluorescent-labeled DNA. The spot with which the fluorescence is generated is detected by a fluorescent scanner or the like, and a fluorescent image is analyzed. Thus, gene expressions, genetic mutations, genetic variations, and the like, can be analyzed.
To develop such DNA microarraying technology, a microarrayer for sequencing spots of DNA fragments densely on a substrate is required.
A microarrayer for sequencing DNA fragments adjusted in advance on a substrate is disclosed in Japanese Patent Laid-Open 503841/1998. In this apparatus, samples are retained in an open capillary flow channel formed between a pair of elongated members while a top end of a head constituted by the pair of elongated members is slightly stamped on a substrate so as to place a spot on the substrate. There is also known a head other than this head. That is, the head is constituted by a solution reservoir portion for retaining a solution, and a placing portion (for example, a pin or a needle) for placing spots on a substrate.
As for the performance of microarrayers, it is a requirement that spots of various DNA samples can be formed quantitatively in given places and with a size ranging from several tens of microns to several hundreds of microns. It is also a requirement that microarrays can be produced quickly in order to produce a large number of replicas.
In such a microarrayer, when a head terminates a work of forming spots of a solution and then retains a next solution different in kind from the previous solution, it is necessary to cleanse the head so as to prevent the previous solution from mixing into the next solution. In the head, there are often provided a plurality of placing portions (for example, pins or needles) for simultaneously forming spots on a plurality of substrates. To prevent the solutions from mixing with each other, all the plurality of placing portions have to be cleansed surely.
When a head which has finished a work of forming spots of a solution is made to retain a next solution of another kind in such a microarrayer, it is necessary to cleanse and dry the head so as to prevent the previous solution from mixing into the next solution. That is, a work of cleansing and drying the head becomes essential after the work of forming spots.
The work of forming spots is however suspended during the work of cleansing and drying the head. In addition, the time required for the work of cleansing and drying is generally longer than the time required for the work of forming the spots. It is therefore difficult to improve the working efficiency.